In Night, Elie Wiesel tells of arriving at Auschwitz, a concentration camp. Initially, Elie was happy to be able to stay with his father, but his happiness quickly turns to fear and dread when one of the prisoners says, "Poor devils, you're going to the crematory." (Wiesel 30)
Up ahead, Elie can see a pit from which flames are leaping. He can tell that something is burning but isn't sure what it is right away. As they continue to walk toward the pit, a truck pulls up, and Elie sees children, some of them just babies, being thrown into that fiery pit.
At the last moment, Elie, his father, and the other prisoners with them are turned toward a different direction, but the impact of those flames devouring children is seared into his brain. The flames in his words "Never shall I forget..." are those flames. They are also the figurative (and literal) flames of the Holocaust that murdered over six million Jews.